ENERGY STAR & IECC climate-zone checker
Enter a window’s NFRC U-factor and SHGC and your climate zone to see whether it meets the LABELED ENERGY STAR 7.0 criteria and the IECC 2021 code minimum.
A U 0.28 / SHGC 0.30 window meets the LABELED IECC zone 5 minimum and does not meet ENERGY STAR North-Central. ENERGY STAR is stricter than the IECC code minimum; both are LABELED published snapshots — confirm the current ENERGY STAR criteria and your local energy code, and use the product’s NFRC-rated numbers, not the marketing sticker.
Calculator inputs
Two different bars apply to a replacement window. ENERGY STAR is a voluntary efficiency label that is stricter than code; the IECC (International Energy Conservation Code) is the code minimum many jurisdictions adopt. This checker compares the product’s NFRC-rated U-factor and SHGC against both, using the LABELED ENERGY STAR 7.0 zone criteria and the IECC 2021 fenestration limits from the climate-zone requirements table.
ENERGY STAR splits the country into four zones (Northern, North-Central, South-Central, Southern). Northern zones cap U-factor tightly (and set an SHGC floor so you keep some solar gain); Southern zones cap SHGC tightly to reject heat. A window can clear the IECC code minimum yet still miss ENERGY STAR — the checker flags each independently.
Formula
Each check is a pass/fail against the labeled limits for the zone:
ENERGY STAR pass ⇔ U ≤ Umax and SHGC within the zone’s min/max
IECC pass ⇔ U ≤ Umax and (SHGC ≤ SHGCmax where required)
Worked example
Example A. A U 0.28 / SHGC 0.30 window in the North-Central zone: IECC zone 5 caps U at 0.30, so 0.28 ≤ 0.30 → meets the IECC minimum. But ENERGY STAR North-Central requires U ≤ 0.25, and 0.28 > 0.25 → does not meet ENERGY STAR.
Example B. A U 0.22 / SHGC 0.25 window in the Northern zone: ENERGY STAR Northern requires U ≤ 0.22 and SHGC ≥ 0.17, and 0.22 ≤ 0.22 with 0.25 ≥ 0.17 → meets ENERGY STAR Northern.
Snapshots, not a compliance sign-off
ENERGY STAR criteria and IECC limits are labeled published snapshots, not a live feed — confirm the current ENERGY STAR version and your local energy code (AHJ) before you order, and always use the product’s NFRC-rated numbers, not a marketing sticker. The ENERGY STAR-to-IECC zone mapping here is a planning convenience; your exact IECC zone is set by county. Meeting a label is not a substitute for a proper whole-building load calculation, which is an HVAC pro’s job.
Reference table
| ENERGY STAR zone | Max U-factor | SHGC | IECC zone | IECC max U |
|---|---|---|---|---|
| Northern | 0.22 | ≥ 0.17 (any) | 6 | 0.30 |
| North-Central | 0.25 | ≤ 0.40 | 5 | 0.30 |
| South-Central | 0.28 | ≤ 0.23 | 3 | 0.30 |
| Southern | 0.32 | ≤ 0.23 | 2 | 0.40 |
LABELED ENERGY STAR 7.0 & IECC 2021 snapshots — full matrix and methodology on the climate-zone requirements table.
Frequently asked questions
What U-factor and SHGC do I need for ENERGY STAR?
It varies by zone. Northern needs U ≤ 0.22 (with SHGC ≥ 0.17), North-Central U ≤ 0.25, South-Central U ≤ 0.28 (SHGC ≤ 0.23), and Southern U ≤ 0.32 (SHGC ≤ 0.23) — labeled ENERGY STAR 7.0 values; confirm the current criteria.
What is the difference between ENERGY STAR and the IECC code minimum?
The IECC is the energy code many jurisdictions enforce; ENERGY STAR is a stricter voluntary efficiency label. A window can pass the IECC minimum and still fall short of ENERGY STAR, so the checker reports both separately.
Which ENERGY STAR zone am I in?
ENERGY STAR groups the US into Northern, North-Central, South-Central and Southern bands. Roughly, the far north is Northern and the deep south is Southern; check the ENERGY STAR zone map for your county, since it is set geographically.
Does meeting ENERGY STAR guarantee my project passes inspection?
No. This is a labeled screening against published snapshots, not a compliance sign-off. Final energy-code compliance is set by your local building code and the AHJ using the product’s NFRC-rated numbers — confirm before you order.